1. Field of the Invention
The invention relates to a low noise converting apparatus suitable for use in a case where, for example, radio waves from a plurality of satellites are received by one parabolic antenna.
2. Description of the Related Art
A satellite broadcasting receiving system is provided with a low noise converter (referred to as an LNB) for converting a signal of a band of, for example, 12 GHz received by a parabolic antenna to an intermediate frequency signal of a band of, for example, 1 GHz and transmitting the signal to an indoor IRD (Integrated Receiver Decoder) or a receiver such as television receiver, VTR, or the like having a receiving tuner of a satellite broadcasting through a connecting cable. FIG. 1 shows an example of such a conventional low noise converter.
In FIG. 1, reference numerals 111 and 112 denote current feeding devices. Radio waves are transmitted from a satellite existing on a geostationary satellite orbit by using a band of, for example, 12 GHz by radio waves having an orthogonal relation, for example, by a horizontally polarized wave and a vertically polarized wave. The radio waves from the satellite are received by a parabolic antenna. The reception signals are inputted to the current feeding devices 111 and 112. The reception signals of the horizontally polarized wave and vertically polarized wave are obtained from the current feeding devices 111 and 112, respectively.
The reception signal of the horizontally polarized wave from the current feeding device 111 is supplied to a low noise amplifier 121. The reception signal of the vertically polarized wave from the current feeding device 112 is supplied to a low noise amplifier 122 and amplified.
Control signals are supplied to the low noise amplifiers 121 and 122 from a control unit 110. Although not shown, a switching signal of the horizontally polarized wave and vertically polarized wave is supplied to the control unit 110 from a satellite tuner. A control is performed so that either the low noise amplifier 121 or 122 is made operative in response to the switching signal. Thus, the switching between the horizontally polarized wave and vertically polarized wave is performed.
An output of the low noise amplifier 121 or 122 is supplied to a low noise amplifier 104 through a coupling circuit 103. The reception signal is further amplified by the low noise amplifier 104. An output of the low noise amplifier 104 is supplied to a filter circuit 105. Unnecessary band components in the reception signal are removed by the filter circuit 105. An output of the filter circuit 105 is supplied to a mixer 106.
A local oscillating signal from a local oscillator 107 is supplied to the mixer 106. In the mixer 106, the reception signal of a band of, for example, 12 GHz is converted to an intermediate frequency signal of a band of, for example, 1 GHz. An output of the mixer 106 is extracted from an output terminal 109 through a high frequency amplifier 108. A signal from the output terminal 109 is supplied to the indoor receiver through a connecting cable.
The conventional low noise converter shown in FIG. 1 receives the signal transmitted from one satellite on the geostationary satellite orbit. The radio waves are transmitted from the satellite by two planes of polarization of the horizontally polarized wave and vertically polarized wave. Therefore, the low noise amplifier 121 for the horizontally polarized wave and the low noise amplifier 122 for the vertically polarized wave are provided for the low noise converter. The switching between the horizontally polarized wave and vertically polarized wave is performed by selectively making the low noise amplifier 121 for the horizontally polarized wave and the low noise amplifier 122 for the vertically polarized wave operative.
In recent years, in association with the development of broadcasting services, a number of satellites were launched. Among the satellites, there are satellites launched to close positions on the geostationary satellite orbit. Signals transmitted from the two satellites launched to close positions on the geostationary satellite orbit as mentioned above can be received by one antenna.
FIG. 2 shows a construction of a conventional low noise converter in the case where the signals from the two satellites existing at close positions on the geostationary satellite orbit are received by one antenna.
In FIG. 2, reference numerals 211 and 212 denote current feeding devices for a reception signal from one satellite and 213 and 214 indicate current feeding devices for a reception signal from the other satellite. The radio waves are transmitted from the two satellites existing at close positions on the geostationary satellite orbit by the horizontally polarized wave and vertically polarized wave by using a band of, for example, 12 GHz. The radio waves from the two satellites are received by one parabolic antenna.
Between the two reception outputs, the signal from one satellite is inputted to the current feeding devices 211 and 212 and the reception signals of the horizontally polarized wave and vertically polarized wave of one satellite are derived from the current feeding devices 211 and 212, respectively. The signal from the other satellite is inputted to the current feeding devices 213 and 214 and the reception signals of the horizontally polarized wave and vertically polarized wave of one satellite are derived from the current feeding devices 213 and 214, respectively.
The reception signal of the horizontally polarized wave of one satellite which is supplied from the current feeding device 211 is sent to a low noise amplifier 221 and amplified. The reception signal of the vertically polarized wave of one satellite which is supplied from the current feeding device 212 is sent to a low noise amplifier 222 and amplified. Control signals are supplied from a control unit 230 to the low noise amplifiers 221 and 222. A switching signal of the horizontally polarized wave and vertically polarized wave is supplied to the control unit 230. A control is performed so that either the low noise 20 amplifier 221 or 222 is made operative in response to the switching signal. Thus, the switching between the horizontally polarized wave and vertically polarized wave is performed.
An output of the low noise amplifier 221 or 25222 is supplied to a low noise amplifier 241 through a coupling circuit 231. The reception signal is further amplified by the low noise amplifier 241. An output of the low noise amplifier 241 is supplied to a coupling circuit 233.
The reception signal of the horizontally polarized wave of the other satellite which is supplied from the current feeding device 213 is sent to a low noise amplifier 223 and amplified. The reception signal of the vertically polarized wave of the other satellite which is supplied from the current feeding device 214 is sent to a low noise amplifier 224 and amplified. Control signals are supplied from the control unit 230 to the low noise amplifiers 223 and 224. The switching signal of the horizontally polarized wave and vertically polarized wave is supplied to the control unit 230. A control is performed so that either the low noise amplifier 223 or 224 is made operative in response to the switching signal. Thus, the switching between the horizontally polarized wave and vertically polarized wave is performed.
An output of the low noise amplifier 223 or 224 is supplied to a low noise amplifier 242 through a coupling circuit 232. The reception signal is further amplified by the low noise amplifier 242. An output of the low noise amplifier 242 is supplied to the coupling circuit 233.
The control signals are supplied from the control unit 230 to the low noise amplifiers 241 and 242. A switching signal of two satellites is supplied to the control unit 230. A control is performed so that either the low noise amplifier 241 or 242 is made operative in response to the switching signal. Thus, the switching between the two satellites is performed.
An output of the coupling circuit 233 is supplied to a filter circuit 225. Unnecessary band components in the reception signal are removed by the filter circuit 225. An output of the filter circuit 225 is supplied to a mixer 206.
A local oscillating signal from a local oscillator 207 is supplied to the mixer 206. In the mixer 206, the reception signal of a band of, for example, 12 GHz is converted to an intermediate frequency signal of a band of, for example, 1 GHz. An output of the mixer 206 is extracted from an output terminal 209 through a high frequency amplifier 208. A signal from the output terminal 209 is supplied to the indoor receiver through a connecting cable.
As mentioned above, the signals from the two satellites existing at close positions on the geostationary satellite orbit can be received by one antenna by providing: the low noise amplifiers 221 and 222 at the first stage for amplifying the reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave which are transmitted from one satellite; the coupling circuit 231 for switching the reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave from one satellite; the low noise amplifier 241 at the next stage for amplifying the reception signal of the horizontally polarized wave or the reception signal of the vertically polarized wave from one satellite; the low noise amplifiers 223 and 224 at the first stage for amplifying the reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave which are transmitted from the other satellite; the coupling circuit 232 for switching the reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave from the other satellite; the low noise amplifier 242 at the next stage for amplifying the reception signal of the horizontally polarized wave or the reception signal of the vertically polarized wave from the other satellite; and the coupling circuit 233 for switching the reception signals of two satellites.
However, if the signals from two satellites are enabled to be received by one antenna as mentioned above, problems such that the number of amplifiers arranged in the low noise converter increases, the number of coupling circuits increases, the costs rise, and it is difficult to realize a small size and a light weight occur.
That is, in the example shown in FIG. 1, since it is intended to receive the signals from one satellite and the signal of the horizontally polarized wave and the signal of the vertically polarized wave from one satellite are transmitted, the reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave are amplified by the low noise amplifiers 121 and 122 and the coupling circuit 103 is provided to select the signal of the horizontally polarized wave and the signal of the vertically polarized wave.
However, in case of enabling the signals from two satellites to be received, since the signal of the horizontally polarized wave and the signal of the vertically polarized wave are transmitted from each satellite, the circuits for amplifying and selecting the signal of the horizontally polarized wave and the signal of the vertically polarized wave and the circuit to switch the satellites are necessary.
That is, in case of enabling the signals from two satellites existing at close positions on the geostationary satellite orbit to be received by one antenna, as shown in FIG. 2, there are necessary: the low noise amplifiers 221 and 222 for amplifying the signal of the horizontally polarized wave and the signal of the vertically polarized wave from one satellite; the low noise amplifiers 223 and 224 for amplifying the signal of the horizontally polarized wave and the signal of the vertically polarized wave from the other satellite; the coupling circuit 231 for switching the signal of the horizontally polarized wave and the signal of the vertically polarized wave from one satellite; the coupling circuit 232 for switching the signal of the horizontally polarized wave and the signal of the vertically polarized wave from the other satellite; the low noise amplifiers 241 and 242 for further amplifying the signals from the satellites; and the coupling circuit 232 for switching the signals of two satellites.
Particularly, providing the three coupling circuits 231, 232, and 233 causes an increase in size when they are mounted.
That is, those coupling circuits are constructed on a microstrip line as shown in FIG. 3. As shown in FIG. 3, the coupling circuit 231 is constructed by extending portions 151, 152, and 153 of strip conductors each having a length of almost xcex/4 (xcex denotes a wavelength at a center frequency of a reception band). The extending portion 151 is extended from an output of the low noise amplifier 221 and the extending portion 152 is extended from an output of the low noise amplifier 222. The extending portion 153 is extended from an input of the low noise amplifier 241. The extending portions 151 and 152 are arranged so as to face the extending portion 153 with predetermined intervals.
As mentioned above, by arranging the extending portion 153 extended from the input of the low noise amplifier 241 so as to face the extending portions 151 and 152 extended from the outputs of the low noise amplifiers 221 and 222, the outputs of the low noise amplifiers 221 and 222 and the input of the low noise amplifier 241 are electrically coupled.
Similarly, as shown in FIG. 3, the coupling circuit 232 is constructed by extending portions 161, 162, and 163 of strip conductors each having a length of almost xcex/4. The extending portion 161 is extended from an output of the low noise amplifier 223 and the extending portion 162 is extended from an output of the low noise amplifier 224. The extending portion 163 is extended from an input of the low noise amplifier 242. The extending portions 161 and 162 are arranged so as to face the extending portion 163 with predetermined intervals.
As mentioned above, by arranging the extending portion 163 extended from the input of the low noise amplifier 242 so as to face the extending portions 161 and 162 extended from the outputs of the low noise amplifiers 223 and 224, the outputs of the low noise amplifiers 223 and 224 and the input of the low noise amplifier 242 are electrically coupled.
Similarly, as shown in FIG. 3, the coupling circuit 233 is constructed by extending portions 171, 172, and 173 of strip conductors each having a length of almost xcex/4. The extending portion 171 is extended from an output of the low noise amplifier 241 and the extending portion 172 is extended from an output of the low noise amplifier 242. The extending portion 173 is extended from an input of the filter circuit 225 (refer to FIG. 2). The extending portions 171 and 172 are arranged so as to face the extending portion 173 with predetermined intervals.
As mentioned above, by arranging the extending portion 173 extended from the input of the filter circuit 225 so as to face the extending portions 171 and 172 extended from the outputs of the low noise amplifiers 241 and 242, the outputs of the low noise amplifiers 241 and 242 and the input of the filter circuit 225 are electrically coupled.
As mentioned above, the coupling circuit comprises the extending portions of the strip conductors each having a length of almost xcex/4 and the position to arrange the coupling circuit is restricted by a circuit construction. Therefore, when the number of coupling circuits increases, an area on a circuit board to construct the coupling circuits increases, a degree of freedom in a layout of circuit parts is small, and a circuit scale is enlarged.
It is, therefore, an object of the invention to provide a low noise converting apparatus which can receive radio waves from a plurality of satellites by one antenna and realize a miniaturization and a reduction in costs.
According to one aspect of the invention, there is provided a low noise converting apparatus comprising: a plurality of first-stage low noise amplifying means each provided in a path of a reception signal of a polarized wave of each of a plurality of satellites; control means for selectively making one of the plurality of first-stage low noise amplifying means operative in accordance with the satellite to be selected and the polarized wave of a radio wave; one next-stage low noise amplifying means for further amplifying an output of the first-stage low noise amplifying means; coupling means for coupling the plurality of first-stage low noise amplifying means and the one next-stage low noise amplifying means; and frequency converting means for frequency converting an output of the next-stage low noise amplifying means.
The reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave of one satellite are amplified by the first-stage low noise amplifiers, respectively. The reception signal of the horizontally polarized wave and the reception signal of the vertically polarized wave of the other satellite are amplified by the first-stage low noise amplifiers, respectively. Outputs of the first-stage low noise amplifiers are selected, coupled by the coupling circuit, and supplied to the next-stage low noise amplifier. With this construction, a plurality of coupling circuits needed in the conventional low noise converter are constructed by one coupling circuit and miniaturized and the costs are reduced. The next-stage low noise amplifier is used in common by one low noise amplifier, the number of parts is reduced, and a construction, connecting lines, and the like are simplified.
According to another aspect of the invention, there is further provided a low noise converting apparatus comprising: coupling means for synthesizing radio waves of different frequencies among radio waves of a plurality of satellites and outputting a synthesized radio wave; first-stage low noise amplifying means for amplifying a reception signal of the plurality of satellites synthesized by the coupling means; next-stage low noise amplifying means for further amplifying an output of the first-stage low noise amplifying means; and frequency converting means for frequency converting an output of the next-stage low noise amplifying means.
For example, in case of receiving signals from two satellites, the reception signals of different frequencies are synthesized and sent to the first-stage low noise amplifier. Thus, the first-stage low noise amplifier is used in common for the reception signals from two satellites and the miniaturization and reduction of costs are accomplished.
The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings.